Light trucks, such as the ordinary pick-up truck, have very little weight on the rear tires when unloaded so that they have very little stability and the rear tires have very little traction, particularly when the truck is being operated on wet, icy or snowy surfaces. When the truck is empty, the rear end portion tends to be too light and has a tendency to skid laterally under slippery conditions. In an attempt to solve this problem, some truck operators load logs or the like in the bed of the truck to provide additional weight on the rear wheels and rear portion of the truck so as to increase the rear tire traction. While the logs or the like do provide additional weight, they must be removed when it is desired to load the truck with other types of cargo.
Recognizing the problems associated with loading and unloading ballast materials from the truck bed when the proper traction conditions are desired, U.S. Pat. No. 2,993,721 discloses the provision of a hollow ballast bumper for pick-up trucks and the like into which water or other liquid can be inserted to provide additional weight on the back end of the truck, and the liquid ballast can be emptied when the truck is loaded. While the compartmentalized bumper of this patent does provide for the use of a liquid ballast to add additional weight to the back end of the truck, the installation of the bumper requires the removal of the conventional bumper. Also, this special type of compartmentalized bumper is relatively expensive and extends outwardly from the rear portion of the truck so that it may provide an obstacle, as well as an unsightly appearance.